Humans are herbivores

Many people think of humans as omnivores, designed to eat a diet with a substantial contribution of nutrients coming from both plants and animals. However, there is strong evidence that humans are in fact herbivores, meaning that the overwhelming majority of their diet should be comprised of plants. This common misunderstanding may well be the leading cause of premature human death worldwide.

What most think of as omnivores, for instance, bears, dogs, raccoons and so on, are in a lineage that descended from dog-like carnivores and should be thought of as carnivores modified to be omnivorous, distinct from herbivores that have been modified to be omnivorous.

Katharine Milton, from the University of California Berkley’s Department of Environmental Science, Policy and Management says “there seems general agreement that the ancestral line leading to apes and humans was markedly herbivorous” and that for most of our approximately 150,000-year existence our diet appears to have been based on plants.

Milton has also pointed out “the lack of evidence supporting any notable diet-related changes in human nutrient requirements, metabolism, or digestive physiology relative to those of great apes.”

Iris F.F. Benzie, D.Phil. at The Hong Kong Polytechnic University, Kowloon argued that we lost the metabolically costly ability to synthesize vitamin C because of the abundance in our ancestors’ diets. Scientists can examine plaque on and isotopes in ancient teeth, fossilized waste and more to learn about what our ancestors ate. Prof. Benzie estimates that our ancestors 10,000 years ago ate around 10 times more vitamin C and fiber than we do today.

William Clifford Roberts, MD and former Editor in Chief of The American Journal of Cardiology argued in a Letter from the Editor that humans are anatomically and physiologically herbivores. Herbivores, he says, have hands or hoofs, flat teeth, long intestines, sweat to cool the body, sip water (cheeks and lips facilitate the creation of a vacuum in the mouth), and get our vitamin C from our diet. Carnivores have claws, sharp teeth, short intestines, pant to cool themselves, lap up water (because they lack cheeks and lips), and make their own vitamin C.

Plants have tough cell walls made of fiber, sugar molecules bonded together, that provides protection and rigidity without using cholesterol. No mammal produces an enzyme that can digest fiber. Instead, herbivores developed a mobile jaw and flat teeth that slide past each other horizontally to chew their food and crush the cell wall, plus a long digestive tract to provide time to extract nutrients.

Carnivore’s food, animal cells, have a flexible, fat-based cell membrane embedded with cholesterol to give it some rigidity. Animal cells are easily digestible but the bones in animals are not, so carnivores have strong stomach acid and a short digestive tract. No chewing is necessary beyond reducing the size of the chunks enough to swallow because there’s no cell wall. As a result, carnivores like cats and omnivorous carnivores like the bear and dog can only move their jaw up and down; their molars slide past each other vertically like a pair of scissors.

Animals like rabbits, cows, and humans can easily move their lower jaw side to side, and most experts agree that humans have generalized herbivorous dentition that, if anything, is best suited for eating seeds.

Heart disease is the leading cause of death in the world according to the World Health Organization. It’s also the leading cause of death in the U.S. according to the CDC, which states that “diets high in saturated fats, trans fats, and cholesterol have been linked to heart disease and related conditions, such as atherosclerosis,” the mechanism underlying most heart disease. Trans-fats and cholesterol are only found in animal foods.

Dr. Roberts points out that “it is virtually impossible… to produce atherosclerosis in the dog” even when feeding them around 200 times the average amount of cholesterol Americans eat daily. Herbivores like rabbits on the other hand “rapidly develop atherosclerosis” if fed comparatively small amounts of fat and cholesterol.

Cholesterol is made from fat, something most plants have little of. Herbivores have evolved to be efficient at producing adequate cholesterol from a low-fat diet. They also have mechanisms that hold onto and recycle fat and cholesterol. When herbivores eat animal-foods, the excessive fat and cholesterol facilitate the formation of atherosclerotic plaques in artery walls.

There is an overwhelming amount of evidence that humans aren’t carnivores like cats or omnivores like dogs but are in fact primarily herbivores. It’s recommended we eat a diet low in saturated fat, trans-fat and cholesterol because of atherosclerosis, a disease that herbivores are susceptible to. The approximately 20-million-year evolutionary lineage of great apes is markedly herbivorous. Our digestive anatomy and physiology, nutrient requirements, and metabolism do not appear to differ notably from the other great apes or herbivores generally, and for most of the approximately 150,000-year history of our species we appear to have eaten mostly plants.

As ever-increasing evidence illuminates this issue, it’s time for humans to consider a change to a plant-based diet.

Sean can be reached at arg-opinion@uidaho.edu

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